(a) Field of the Invention
The present invention relates to light diffusing devices and more particularly to a light diffusing device of obtaining a surface having a uniform brightness of a comparatively large area by using a luminous flux of a small radiating angle.
(B) Description of the Prior Art
Optical fibers utilized as a light emitting diode or a light guide are so small in the light emitting area or irradiated area and are so narrow in the light radiating angle that it is difficult to uniformly irradiate a surface having a comparatively wide area by using such light source means. However, in the display field, it is required to keep a surface having a predetermined area at a uniform brightness. Various methods have been already attempted to meet this requirement. That is to say, there is suggested a method of widening the radiating angle of a light bundle radiated from the end surface of optical fibers or the surface of a light emitting diode by setting an optical lens adjacently to the luminous end of the optical fibers or the luminous surface of the light emitting diode or by embedding a prism of a special shape formed of such synthetic resin favorable in the transparency as an acrylic resin in the luminous end surface of the optical fibers or the luminous surface of the light emitting diode. However, such conventional method has a defect that the area of the surface which can be kept at a uniform brightness is still so narrow that, in case the area is somawhat wider, the brightness will fluctuate.